1. Field of the Invention
This invention relates to a magnetic memory for storing information in a magneto-resistivity effect element.
2. Description of the Related Art
In recent years, the MRAM (Magnetic Random Access Memory) has been attracting attention as a memory cell for use in such information processing devices as computers and communication facilities. Since the MRAM is capable of memorizing data magnetically and therefore maintaining directions of magnetization without having to use any electric means, it can avoid the disadvantage of losing information due to power failure as experienced by the DRAM (Dynamic Random Access Memory) and SRAM (Static RAM) which are volatile memories. The MRAM also excels such conventional nonvolatile memories as the flash EEPROM and the hard disk device in terms of access speed, reliability, and power consumption. The MRAM, therefore, is reputed to be capable of alternating the functions of such volatile memories as DRAM and SRAM and all the functions of such nonvolatile memories as the flash EEPROM and the hard disc devices as well (refer to the official gazette of JP-A-11-274599).
In the development of an information device directed toward the so-called ubiquitous computing which enables information to be processed everywhere at the same time, the desirability of such a memory which fulfills high-speed processing and decreases power consumption as well and permits avoidance of loss of information even in the case of power failure finds general recognition. The MRAM promises to satisfy all these requirements and is expected to find adoption in numerous information devices in the future.
Particularly, cards and portable information terminals which are carried daily by users on their persons often fail to secure sufficient power supply. When a large volume of information is processed under a harsh environment of utility, therefore, even the MRAM which boasts of low power consumption is required to allow further decrease of power consumption during the course of processing information.
As one example of the technique which is capable of further decreasing power consumption in the MRAM, the magnetic memory which is published in the official gazette of JP-A2000-90658, the official gazette of JP-A2004-128430, or on page 133 of the Nov. 18, 2002 issue of the “Nikkei Electronics” is now available. This magnetic memory is provided in each of the individual memory regions (memory cells) thereof with a bit line, a word line disposed perpendicularly to the bit line, and a tunneling magneto-resistivity effect (TMR) element disposed between the bit line and the word line at the position of intersection thereof. Further, this magnetic memory is provided near the TMR element in the bit line or the word line with a yoke (magnetic field controlling layer) serving to surround the wire. The yoke is formed of a ferromagnetic body of high magnetic permeability and enabled to fulfill the role of abating the leakage of a magnetic flux from the bit line or the word line and concentrating the magnetic flux on the TMR element. As a result, the magnetic field necessary for the inversion of the state of magnetization of the TMR element can be attained even with a low power consumption. Further, the magnetic flux can be concentrated on the TMR element.
Incidentally, the TMR element is furnished with a first magnetizing layer (magnetic susceptibility layer) enabled to change the direction of magnetization by an external magnetic field, a second magnetic layer having a fixed direction of magnetization, and a non-magnetic insulating layer interposed between the first magnetic layer and the second magnetic layer and is adapted to memorizes binary data by controlling the direction of magnetization of the first magnetic layer parallel or not parallel to the direction of magnetization of the second magnetic layer.
A further study made by the present inventor, however, has ascertained that even the magnetic memory adopting the yoke is not always free from the possibility of failing to save power consumption. The yoke rather threatens such problems as needing large power consumption for generating a magnetic field and, owing to the influence of an inner magnetic field of its own, hindering magnetic memory when it happens to have a shape lacking due consideration.
Since the TMR element is so configured as to memorize binary data by inverting the direction of magnetization of the magnetic layer, it becomes important to enable the power consumption needed for the inversion of this direction of magnetization to be well balanced in the two directions pertinent herein. The low power consumption is not substantially attained, for example, where the inversion of magnetic field in one direction adds to power consumption while the inversion of magnetic field in the other direction induces a decrease of power consumption. The adoption of the yoke, therefore, has entailed the problem of complicating the control of electric current and the timing control during the course of writing operation when the directions of magnetization of the yoke are deprived of good balance.
When the yoke suffers occurrence of a multiplicity of magnetic domains therein, the variation of the states of magnetization of the bit line and the word line results in emitting Barkhausen noise, a fact which constitutes a cause for deteriorating the writing property.
This invention, originated in the light of the problems enumerated above, is directed toward abating the dispersion of the writing magnetic fields while reducing the power consumption needed during the course of writing in the magnetic memory.